1. Field of the Disclosure
The present disclosure relates generally to geological exploration in wellbores. More particularly, the present disclosure describes an apparatus, a machine-readable medium, and a method useful for obtaining measurements made in crossed-magnetic fields that can be used to determine formation properties.
2. Description of the Related Art
A variety of techniques are currently utilized in determining the presence and estimating quantities of hydrocarbons (oil and gas) in earth formations. These methods are designed to determine formation parameters, including, among other things, the resistivity, porosity, and permeability of a rock formation surrounding a wellbore drilled for recovering the hydrocarbons. Typically, the tools designed to provide the desired information are used to log the wellbore. Much of the logging is done after the wellbores have been drilled.
Extensive work has been done in the determination of formation properties using nuclear magnetic resonance (NMR) methods. In the NMR method, a magnetic field is applied to formation which aligns the nuclear spins in a direction parallel to the magnetic field. The formation is then pulsed with a pulsed radio frequency magnetic field orthogonal to the static magnetic field which changes the direction of the nuclear spins. Signals resulting from precession of the nuclear spins are measured, and with proper selection of the pulsing parameters, various formation properties such as porosity and diffusivity can be measured. There has been little recognition of measurements other than NMR measurements that can be made in crossed-magnetic fields. U.S. patent application Ser. No. 11/696,461 of Tabarovsky et al., having the same assignee as the present disclosure and the contents of which are incorporated herein by reference, teaches and claims a method of determining a resistivity parameter of an earth formation through casing using acoustic measurements in crossed-magnetic fields. The present disclosure is related to determination of other properties using measurements in crossed-magnetic fields.